The neuronal growth associated protein GAP-43 has been implicated in the modulation of neural plasticity during development and learning. We propose to examine and manipulate the expression of GAP-43 in the olfactory bulb during early learning. First, we will examine the expression of GAP- 43 in the olfactory bulb during postnatal development by RNA blots, RNAse protection quantification, in situ hybridization, and immunocytochemistry. Because phosphorylation of GAP-43 by protein kinase C is critical for the function of this protein, and because recent data suggest that protein kinase C may stabilize GAP-43 mRNA, we will also analyze the expression of the protein kinase C isozymes in the bulb during development. These same analyses will be performed on the olfactory bulbs from animals that have undergone olfactory preference training. Extracellular dopamine has been shown to increase in the neonatal olfactory bulb during early olfactory preference acquisition. Data from our laboratory suggests that the release of dopamine is modulated by GAP-43. Hence, we postulate a link between GAP-43 expression and dopamine levels in the olfactory bulb. Proposed genetic intervention experiments to test for this relationship include injection of Herpes Simplex Virus One (HSV-1) GAP-43 recombinants in vivo into the olfactory bulb and the construction of transgenic mice expressing a GAP-43 mutant. We will use HSV-1 vectors expressing GAP-43 antisense RNA to decrease the expression of GAP-43 in dopaminergic glomerular-layer cells in the olfactory bulb during olfactory preference learning, and assay the injected rats by 2-deoxyglucose uptake, in vivo dialysis, and behavioral preference to determine the consequences of such genetic intervention. We will also use HSV-1 vectors to overexpress GAP-43 in the olfactory bulb after the sensitive period for olfactory preference learning, to determine whether this manipulation will allow expression of any of the neural or behavioral correlates of early odor preference acquisition. Finally, we will construct transgenic mice expressing, under the control of the tyrosine hydroxylase promoter, a mutant of GAP-43 in which the serine-41 that is normally phosphorylated by protein kinase C is replaced by a glycine residue. The aim is to cause deficiency in dopamine release in dopaminergic neurons expressing this mutant. We will examine the effects of such a mutation on early olfactory learning in transgenic mice.